Try a different application to burn the data DVD's.It sounds like something is wrong with the method you are burning the discs or possible with Nero.I'm guessing it's just the settings you are using in Nero though.

I still haven't been able to fix this problem 5 months down the track... Have tried Ritek G04 DVD-Rs and also Taiyo Yuden DVD-Rs (burnt on Pioneer DVR107), but to no avail. My old Pioneer DVD104S still won't read the data discs... The drive is supposed to support DVD-Rs, I don't really want to buy another DVD-ROM just so I can play my burnt DVDs!